Process for preparing cyclopropane



Patented July 9, 1940 rnocsss FOR PREPARING GYCLOPROPANE John M. Ort,Rockville Centre, N. Y., assignor to E. R. Squibb & Sons, New York, N.Y., a corporation of New York-v No Drawing. Application June 23, 1939,

Claims.

This invention relates to, and has for its object the provision of, animproved process for the production of cyclopropane.

Cyclopropane has heretofore been prepared by J the treatment of atrimethylene dihalide with a metal reduction agent in aqueous alcohol,e. g. by the reaction of trimethylene dibromide with zinc in about 86%ethanol (Lott and Christiansen, Jour. A. Ph. A., 19 (1930) 341). Thisprocedure has been improved-With respect to reaction time and yieldbyefiecting the reaction in the presence of a catalyst or activatorconsisting of a small proportion of a dissolved salt of a metal such asiron, copper, cobalt, nickel, vanadium,

chromium or manganese, as described an"d claimed in the copendingapplication of W. A. Lott, Serial No. 139,987, filed April 30, 1937.

' These activators, however, were found to decrease in power as thewater content of the reaction mixture was increased, and to be lesseffective when using trimethylene chlorobromide thantrimethylenedibromide. It became desirable, therefore, to find morepowerful activators. especially activators capable of overcoming thereduced reactivity of the reactants in essentially aqueous reactionmedia (i. e. media constituted in major proportion, or entirely, ofwater) It has been found that the dissolved salts of noble metals, interalia platinum, gold, and notably silver, are powerful activators for thereduction of trim'ethylene dihalides to cyclopropane, enabling, forexample, the production of cyclopropane at a practical rate ofevolution,

from trimethylene chlorobromide in an essentially-aqueous reactionmedium. By dissolved salts is meant, of course, salts in solution in thereaction medium. Since these activators-even more than those disclosedin the Lott application, also catalyze the secondary, hydrogen-formingreaction, there should preferably be added to the reaction medium asmall proportion of an alkali, notably Mg(OI-I) 2, (as described andclaimed in my -copending application Serial No. 280,847 filedsimultaneously herewith).

The invention is applicable generally to the production of cyclopropaneby the reduction of trimethylene dihalides, notably the dibromide andchlorobromide; the utilizable metal reduction agents include, interalia, zinc, iron and magnesium; the reaction medium may range incomposition from the conventional essentiallyalcoholic (lower aliphaticalcohol, e. g., methyl ethyl, or isopropyl) to the essentially-aqueous,and other alkalies may be used in place of I Serial No. 280,848

Mg(OH)2, for example, NaOH, Ca(OI-I) 2 or NazCOa.

The dissolved salts of noble metals are effective activators in minuteproportion, about 0.1 g. of A AgNOa, forexample, being an efiectiveactivator for 1 kg. zinc dust. The optimum amount of activator isdependent on the temperature, pH, alcohol content and time of reaction,lower temperatures and the presence of a small amount of alcohol beingpreferred. In view of the small proportion of noble metal salt used andthe relatively high cost of the trimethylene dihalide, recovery of theactivator from the reaction mixture is not required.

The following examples are illustrative of the invention (theingredients-especially the noble metal salt-being mixed in the givensequence, and the noble metal salt being added in rather dilutesolution, slowly, with stirring):

Example 1 A mixture of the followingf Distilled water cc 400 95% ethanolcc 40 Zinc dust g 200 Aqueous AgNOs solution containing 0.0175 g.

AgNOs cc 335 NaBr g 8 Dry Mg(OH)2 1 g is heated at about -90 C. and 454g; trimethylene dibromide is added slowly so as to produce the desiredrate of evolution of cyclopropane; an about yield is obtained, theevolved gases containing less than 2% hydrogen.

is heated at about 80-90 C. and 454 g. trimethylene chlorobromide isadded slowly so as to produce the desiredrate of evolution ofcyclopropane; a 93% yield is obtained, the evolved gases containing anegligible amount of hydrogen.

is heated at about -90 C. and 125 g. trimet'hylene chlorobromide isadded slowly so as to produce the desired rate of evolution ofcyclopropane; a 56% yield is obtained, the evolved gases containing 12%hydrogen.

Example 4' A mixture of the following:

Distilled water 'cc 300 i 1% aqueous solution of AgNOs cc 5 Ethanol cc20 Iron powder g 65 NaBr g 3 Mg(Ol-I) 2 g 20 is heated at about 80-90 C.and 95 g. trimethylene chlorobromide is added slowly so as to producethe desired rate of evolution of cyclopropane; a 73% yield is obtained,the evolved gases containing 6% hydrogen.

Example 5 A plant-scale production of cyclopropane is carried out asfollows: gallons of distilled water and 240 pounds of zinc dust areplaced in a jacketed, internally zinc-coated'still and briskly agitated;then '74 g. of 'AgNoa dissolved in 25 gallons of distilled water isadded gradually to the swirling contents in the still, and then 10pounds of NaBr is added and dissolved, followed by 45 pounds dryMg(OII)-2 and 8 gallons of ethanol; the still is then closed and steamadmitted to the jacket until the temperature of the reaction mixturereaches about 50 C., whereupon the steam is cut off and the slowaddition of 400 pounds of trimethylene chlorobromide begun; the reactionbeing exothermic, cold water is passed into the jacket to prevent the:temperature rising above 60 C., and the rate of addition of thechlorobromide is increased periodically until it reaches about poundsper hour. The evolved cyclopropane is recovered in over 83% yield with alow hydrogen content.

The residue in the still is filtered while still warm in order to getthe filtrate for bromide recovery, the filtration proceeding smoothlyand rapidly despite the presence of Zn(OI-I)2 and some Mg(OI-I)2. TheMg(OH)2 in addition greatly reduces the acidity of the reaction mixwhichcomprises reacting a trimethylene dihalide with a metal reduction agentin the presence of a dissolved salt of a noble metal.

2. The process of preparing cyclopropane which comprises reacting atrimethylene dihalide with a metal reduction agent in anessentially-aqueous reaction medium in the presence of a dissolved saltof a noble metal.

3. The process of preparing cyclopropane which comprises reacting atrimethylene dihalide with a metal reduction agent in the precence of analkali and of a dissolved salt of a noble metal.

4. The process of preparing cyclopropane which comprises reacting atrimethylene dihalide with a metal reduction agent in anessentially-aqueous reaction medium in the presence of an alkali and ofa dissolved salt of a noble metal.

5. The process of preparing cyclopropane which comprises reacting atrimethylene dibro-mide with a metal reduction agent in anessentially-aqueous reaction medium in the presence of an alkali and ofa dissolved salt of a noble metal.

6. The process of preparing cyclopropane which comprises reacting atrimethylene chlorobromide with a metal reduction agent in anessentiallyaqueous reaction medium in the presence of an alkali and of adissolved salt of a noble metal.

'7'. The process of preparing cyclopropane which comprises'reacting atrimethylene dihalide with zinc in the presence of a dissolved salt of anoble metal.

8. The process of preparing cyclopropane which comprises reacting atrimethylene dihalide with zinc'in an essentially-aqueous reactionmedium in the presence of Mg(OI-I)2 and of a dissolved salt of a noblemetal.

9. The process of preparing cyclopropane which comprises reacting atrimethylene dihalide with zinc in an essentially-aqueous reactionmedium in the precence of Mg(OH)2 and of a dissolved silver salt.

10. The process of preparing cyclopropane which comprises reacting atrimethylene dihalide with zinc in an essentially-aqueous reactionmixture in the presence of Mg(OH)2 and of AgNOs. v

JOHN M. CRT.

